A.O. Smith Error Code E3: Sensor Fault

Severity
Warning
Type
digital display
Estimated repair cost: $100 — $250 (parts + labor)
Warning: Your A.O. Smith water heater has detected a sensor fault, which will prevent it from operating. You will have no hot water until this is resolved.

How to Fix A.O. Smith Code E3

  1. Step 1: Check the display for any other error codes that might give more specific information about the sensor at fault.
  2. Step 2: Try resetting the water heater by turning off the power at the breaker for a few minutes, then turning it back on. This might clear a temporary fault.
  3. Step 3: If the error persists, contact a qualified HVAC technician or plumber to diagnose and repair the issue. Do not attempt to disassemble the unit yourself.

How to Reset A.O. Smith Code E3

  1. Turn off the unit using the power button on the front panel.
  2. Turn off the gas supply valve.
  3. Turn off the circuit breaker supplying power to the unit. Wait 30 seconds.
  4. Restore power at the breaker, then open the gas valve.
  5. Turn the unit back on. If the error returns, the underlying issue needs repair.

What does E3 mean?

The E3 error code on your A.O. Smith tankless water heater indicates a problem with one of its temperature sensors. These sensors are vital for monitoring water temperature and ensuring the unit operates safely and efficiently. The heater's control board relies on accurate readings from these sensors to regulate the burner and prevent overheating. When the control board detects a faulty sensor signal (either an open circuit, short circuit, or out-of-range reading), it shuts down the unit and displays the E3 error code.

This shutdown is a safety measure to prevent potential damage to the unit or, in rare cases, unsafe operating conditions. The specific sensor causing the issue needs to be identified and replaced to restore normal operation. Because this error locks out the water heater, you won't have hot water until the problem is resolved.

Affected Models

Replacement Parts

PartOEM NumberEst. Cost
Thermistor (various types) — —
Wiring harness — —
Control board — —

Related Codes on Same Models

CodeDescriptionSeverity
E1 Thermistor Failure Warning
E2 Dry Fire Protection Warning
E4 High Temperature Cutoff Critical
E5 Communication Error Warning
E06 Flammable Vapor Detection Critical
ECO Emergency Cutoff Critical
LOC Controls Locked Warning
UPR Upper Element Fault Warning
LWR Lower Element Fault Warning